Production of high-quality ingots



March 15, 1966 P. G. TURNER PRODUCTION OF HIGH-QUALITY INGCTS Filed Aug. 5, 1965 FI'G.1

FIG.2.

United States Patent 3,239,898 PRODUQTRUN 0F HIGH-QUALITY INGOTS Philip G. Turner, Wormelow, England, assignor to The International Nickel Company, Inc, New York, N.Y., a corporation of Delaware Filed Aug. 5, i963, Ser. No. 299,810 {Claims priority, application Great Britain, Aug. 8, 1962, 30,404/62 7 Claims. (Cl. 22209) The present invention relates to production of ingots of high melting point metals and, more particularly, to production of ingots of high nickel alloys containing chromium, aluminum and/ or titanium.

It is well known that in the casting of metals of high melting point into ingot molds it is common to find that the ingot has a surface layer containing substantial quantities of nonmetallic inclusions. The origin of these inclusions is not certain, one possibility being that they are the result of splashing or turbulence and another being that they are introduced by the repeated use of scrap as a constituent of the charge. The surface layer containing these inclusions must be removed by machining, thus adding to the expense of the production of a final product. If the casting is put into an extrusion press and extruded, or is rolled into bar, the inclusions show themselves as stringers in the extruded or rolled product unless they are first removed.

Surface layers which contain nonmetallic inclusions are commonly found in ingots cast by pouring metal from a ladle into an ingot mold. Also, this type of surface layer is found in ingots produced by the Durville process, in which the molten metal is poured into a receiver of a combined receiver and mold which is thereafter rotated in a vertical plane to cause the metal to flow from the receiver into the mold. When it is not possible or convenient to use a normal slag in the receiver, there is a considerable tendency for the undesirable surface layer to form.

In order to produce metal ingots of improved quality it has been proposed in the prior art to cast metal for ingots by pouring onto and/or through a body of nonmetallic material which is deposited in the bottom of the ingot mold before or during casting. Nonmetallic materials which have been proposed for such use in ingot molds include powdered solid slag, fiber glass, diatomite, molten slag, charcoal, shavings, braids of rope and mats of paper or cork. In practical commercial operation, the degree of success achieved in producing ingots of high quality by casting metal through a nonmetallic material is dependent upon many factors, including the characteristics of the nonmetallic material and the composition of the metal which is cast. All of the materials of the prior art do not function equally well in the casting of all metals. Difficulties in production of ingots of high nickel alloys containing chromium, aluminum and/or titanium are espectially great and, insofar as I am aware, casting processes of the prior art have not proven to be entirely satisfactory for commercial production of ingots of high nickel alloys containing chromium, aluminum and titanium. Although attempts were made to overcome the foregoing difficulties and other disadvantages, none, as far as I am aware, was entirely successful when carried into practice commercially on an industrial scale.

A new process has now been discovered whereby metal ingots of improved quality can be cast.

It is an object of the present invention to provide a new process for producing metal ingots.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing in which:

r 3,239,898 Patented Mar. 15, 1966 I ice FIGURE 1 is a reproduction of a photograph of a half cross section of an ingot produced in accordance with the invention; and

FIGURE 2 is a reproduction of a photograph of a half cross section of an ingot produced by a process of the prior art.

Generally speaking, the present invention contemplates the production of metal ingots by a new process wherein molten metal prepared for ingot casting is poured through a body of special loose granular material to produce ingots having improved characteristics of quality including a high degree of freedom from inclusions. The special body employed in the process of the invention is a body of vermiculite of a depth of at least four inches, advantageously at least seven inches, which is initially placed in the bottom of a metal receiver, e.g., an ingot' mold. This special body is of loose granular vermiculite, i.e., the vermiculite is in granular form and the granules are not compacted or bound together. Advantageously, after the metal is poured, a layer of vermiculite of at least about four inches depth is retained on top of the metal until the metal is solidified.

In carrying the invention into practice to produce ingots by pouring molten metal into a vertically disposed ingot mold it is advantageous to deposit a body of vermiculite of at least seven inches depth in the ingot mold before casting. Molten metal for the ingot is thereafter poured through the vermiculite into the ingot mold. By providing that the depth of vermiculite be at least seven inches, advantageous results are obtained through having a longer contacting path of vermiculite with the stream of metal, a greater volume of vermiculite to control splash and a much higher insulation value.

Vermiculite granules of the vermiculite body through which molten metal is poured in accordance with the invention are generally of a size of about inch to about A inch, e.g., at least about of the vermiculite is of particles having a maximum dimension of about A; inch to about A inch.

According to the present invention the molten metal is poured into and through a body of vermiculite. Vermiculite is exfoliated mica and it is well known as a lightweight refractory insulating material. The molten metal causes a small amount of vermiculite to melt and form a slag, the remainder of the vermiculite rising to the surface and floating on its own slag. The vermiculite prevents splash during the pouring since the metal passes down through it, and it also forms a slag covering. By proceeding according to the invention one is enabled to produce castings substantially free from nonmetallic inclusions in the surface layers. The improvement in quality obtained as a result of producing an ingot in accordance with the invention instead of by a prior art process is evident by comparison of FIGS. 1 and 2 of the accompanying drawing. Both of these figures are reproductions of photographs of transverse sections of ingots of about seven inches diameter and of a high nickel alloy containing about 18% to about 21% chromium, about 0.5% to about 1.8% aluminum, about 1.8% to about 2.7% titanium, up to about 0.1% carbon, up to about 5% iron, up to about 2% cobalt, up to about 1% silicon, up to about 1% manganese with the balance substantially nickel. All percentages expressed herein are weight percentages. Undesirable peripheral discontinuities and/or inclusions are clearly apparent in the ingot of FIG. 2 which was cast similarly to the process used for the ingot of FIG. 1 but without using vermiculite. The ingot of FIG. 1, which was produced by pouring through vermiculite in accordance with the invention, is of improved quality as compared with the ingot of FIG. 2 in that the ingot of FIG. 1 is free from the undesirable peripheral 3 discontinuities and/ or inclusions present in the ingot of FIG. 2.

An additional advantage of the process of the invention is that the vermiculite resting on the top of the molten metal during solidification retards the solidification and gives time for fine nonmetallic particles to escape from the melt and pass into the slag, so that the castings are cleaner than usual.

In the application of the invention to casting by the Durville process, the vermiculite is put in the receiver. It has been found that a substantial body of vermiculite is necessary, and that success is not achieved if there is only a shallow layer, say two inches deep. The layer should be at least four inches deep and a depth of seven inches or more is advantageous. Normally excellent results are obtained if the vermiculite is in the receiver alone, but if desired it may also be put in the ladle as well, so that the metal teemed from the furnace will pass into and through it in the ladle.

In casting by other processes, e.g., teeming into a ladle and pouring from the ladle into an ingot mold, the vermiculite can be put in the ingot mold, or into both the ladle and mold.

A substantial proportion of the vermiculite can be recovered at the end of the process, e.g,. by the application of suction through a pipe or by winnowing.

Metals of high melting point which can be treatedv by pouring into and through vermiculite according to the invention broadly include any metal having a melting point of 1300 C. and over, and specifically steel, both unalloyed and alloyed, and alloys of high nickel content. The invention is particularly useful with alloys containing chromium, aluminum or titanium, because the oxides of these metals both are stable and form mechanically strong films in the molten metal, and these films tend to collect other nonmetallic inclusions and so to form agglomerates.

In casting ingots of high nickel alloys containing at least about 40% nickel, at least about chromium and small amounts of aluminum and/or titanium, e.g., about 1% to about 10% of metal from the group consisting of aluminum and titanium, in accordance with the invention such an alloy is advantageously cast at a temperature in the range of from about 1350 C. to about 1600 C. through a body of vermiculite of at least four inches depth.

For the purpose of giving those skilled in the art a better understanding of the invention and a better appreciation of the advantages of the invention, the following illustrative examples are given:

EXAMPLE I A body of vermiculite in accordance with the invention of a depth of about eight inches is deposited in an ingot mold of about seven inches in internal diameter and about ten inches in depth. About 150 pounds of an alloy containing about 20% chromium, about 1.5% aluminum, about 2.5% titanium, about 16% cobalt, about 0.08% carbon, about 1% iron with the balance substantially nickel and at a temperature of about 1550 C. is cast onto the vermiculite body in the mold and the metal passes through the vermiculite body. Thus, the metal is cast through the vermiculite. The metal fills the mold to a depth of about ten inches and. the vermiculite floats on top of the metal. A small amount of the vermiculite, e.g., up to of the order of about 10%, melts and forms a slag. A substantial body of unmelted vermiculite at least about four inches deep remains on top of the metal in a refractory collar (hot top) after casting is completed. The

metal solidifies into an ingot with the vermiculite on top of the metal. After the ingot has cooled the ingot is found to be substantially free from undesirable peripheral discontinuities and inclusions.

EXAMPLE II A body of vermiculite in accordance with the invention of a depth of about 12 inches is deposited in a heated receiver of a Durville apparatus measuring about 18" x 18" x 12". About 600 pounds of a high nickel alloy containing about 15% chromium, about 4.5% aluminum, about 1.2% titanium, about 20% cobalt, about 5% molybdenum, about 0.15% carbon, about 2% iron with the balance substantially nickel and at a temperature of about 1550 C. is poured onto the vermiculite body in the receiver and the metal passes through the vermiculite body. Thus, the metal is poured through the vermiculite. The metal fills the receiver to a depth of about eight inches and the vermiculite floats on top of the metal. A small amount of the vermiculite melts and forms a slag. A substantial body of unmelted vermiculite at least about eight inches deep remains on top of the metal after the pouring. The bulk of the vermiculite is then scraped off and the receiver tilted. The metal from the receiver now runs into the molt under the thin covering layer of vermiculite. The metal solidifies into an ingot with the vermiculite on top of the metal. After the ingot has cooled the ingot is found to be substantially free from undesirable peripheral discontinuities and inclusions.

Vermiculite in the physical form in which it is used in accordance with the invention is sometimes referred to as expanded vermiculite. In practicing the present invention it is advantageous to use vermiculite derived from a type of mica having a typical chemical composition similar to the composition set forth in the following table.

1 Free and combined water.

The present invention is particularly applicable to producing high melting point (1300 C., or higher) alloy castings which are substantially free from undesirable peripheral discontinuities and inclusions. The invention is applicable to the production of sound clean ingots of alloys containing nickel and chromium including stainless steels and high melting point alloys containing about 7% to about 90% nickel, about 10% to about 30% chromium and up to about iron and is specially applicable to production of sound clean ingots of heat resisting alloys such as high melting point alloys containing at least about 40% nickel, about 10% to about 30% chromium, about 1% to about 10% of aluminum and/or titanium, up to about 30% cobalt, up to about 6% molybdenum, up to about 5% iron, and up to about 0.2% carbon.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

I claim:

1. In a process for producing an ingot of a metal having a melting point of at least 1300 C. comprising pouring said metal in a molten condition through a body of nonmetallic material, the improvement which comprises conducting the pouring by pouring said molten metal through a body of loose granular vermiculite which is at least four inches deep.

2. In a process for casting an ingot of a metal having a melting point of at least 1300 C. in an ingot mold, the improvement which comprises providing a body of loose granular vermiculite of at least four inches depth in the ingot mold, casting said metal in a molten condition through said body of vermiculite and retaining a layer of vermiculite of at least four inches depth on top of the metal until the metal is solidified.

3. A process for producing an ingot of metal characterized by a melting point of at least 1300" C. which comprises pouring said metal for an ingot through a body of loose granular vermiculite which is at least four inches deep.

4. A process as set forth in claim 3 wherein the metal is poured through a body of vermiculite which is at least seven inches deep.

5. A process as set forth in claim 3 wherein at least 80% of the loose granular vermiculite is of a particle size having a maximum dimension of about /8 inch to about 4 inch.

6. A process for casting a heat resisting alloy ingot which comprises pouring an alloy characterized by a melting point of at least 1300 C. and containing at least about nickel, about 10% to about 30% chromium, about 1% to about 10% of metal selected from the group consisting of aluminum and titanium, up to about 30% cobalt, up to about 6% molybdenum, and up to about 0.2% carbon at a temperature of from about 1350 C. to about 1600 C. through a body of loose granular vermiculite at least four inches deep.

7. A process as set forth in claim 6 wherein the alloy is poured through a body of loose granular vermiculite which is at least seven inches deep with at least of the vermiculite being of particles having a maximum dimension of about /s inch to about inch. 

3. A PROCESS FOR PRODUCING AN INGOT OF METAL CHARACTERIZED BY A MELTING POINT OF AT LEAST 1300*C. WHICH COMPRISES POURING SAID METAL FOR INGOT THROUGH A BODY OF LOOSE GRANULAR VERMICULITE WHICH IS AT LEAST FOUR INCHES DEEP. 